This invention relates in general to the field of electronic devices. More specifically, the invention relates to a system and method for controlling vapor dryer processing which is used in the fabrication of semiconductor devices.
Vapor dryers are often used in semiconductor fabrication processing. Typically, a boat loaded with semiconductor substrate wafers is placed into a vapor dryer chamber. Heaters along the bottom and/or sides of the vapor dryer chamber heat a drying medium, typically isopropyl alcohol (IPA), to create a vapor cloud of drying medium within the chamber. Cooling coils within an upper portion of the vapor dryer chamber are typically provided to condense the drying medium vapor. When the vapor dryer chamber reaches an equilibrium or steady state, the vapor cloud develops an upper boundary within the vapor dryer chamber known as a vapor blanket.
The boat and semiconductor substrate wafers preferably rest in the chamber beneath the vapor blanket. The drying medium acts to displace water or other fluid associated with the semiconductor substrate wafers. If water is not displaced from the semiconductor substrate wafers, water can inhibit the effectiveness of subsequent fabrication processes. For example, if not removed, water may etch a silicon wafer. Water may also collect and leave behind a deposit when it eventually evaporates. The deposit often creates a defect. Water may react with the substrate material such that deposited material fails to properly adhere to the substrate. These types of defects are often referred to as watermarks.
A variety of factors can disrupt the effectiveness of the vapor drying process. Often, before a boat and semiconductor substrate wafers are placed into the vapor dryer chamber, the chamber has reached an equilibrium or steady state and developed a vapor blanket at a desired height within the vapor dryer chamber. When the lid of the vapor dryer chamber is opened, the vapor cloud is disturbed and the vapor blanket no longer rests at the desired height within the vapor dryer chamber. The vapor cloud may only partially cover the semiconductor substrate wafers such that the vapor cloud interacts with only a portion of the wafers. Eventually the vapor dryer chamber may return to its initial equilibrium or steady state with the vapor blanket resting at the desired height within the vapor dryer chamber. However, a portion of the substrates may not be properly processed because of the disruption of the vapor blanket.
Other factors can effect vapor dryer processing. The number of disks within the chamber can effect the time it takes for the chamber to return to its equilibrium state. The heater or cooling coils may malfunction such that the vapor cloud does not develop properly. An adequate amount of drying medium may not be available to process the substrate wafers. Also, an exhaust system associate with the vapor dryer chamber may malfunction, disrupting vapor dryer processing.
Often vapor drying processes are timed. After being processed within the vapor dryer chamber for a desired amount of time, the boat and substrate wafers are removed. One problem with using a set time is that the wafers may not be properly processed if the chamber does not return to its equilibrium state as quickly as expected. Also, if the heater or cooling coils are malfunctioning, the substrate wafers may not be processed properly. Because it often takes days or weeks to discover a watermark and its source, improper processing can waste valuable time and resources.
Set times are typically conservative, often resulting in the substrate wafers remaining within the vapor dryer chamber for a longer period than is necessary for optimum processing. This practice consumes valuable process time within the chamber that could be used to process other semiconductor substrate wafers.
In accordance with teachings of the present disclosure, a system and method are provided for controlling vapor dryer processing that substantially eliminates or reduce disadvantages and problems associated with prior systems and methods for operating a vapor dryer. The vapor dryer system preferably includes a vapor dryer chamber with a lid. A heater may be disposed within the vapor dryer chamber to heat a selected liquid drying medium, such as IPA, in the bottom of the vapor dryer chamber. Cooling coils may be disposed within an upper portion of the vapor drying chamber condense drying medium vapor. A vapor monitor is preferably disposed within the vapor dryer chamber to monitor the vapor concentration at a desired position. A controller is preferably associated with the vapor monitor and evaluates vapor concentration measurements from the vapor monitor.
In one aspect of the present invention, a vapor dryer system for use in semiconductor fabrication includes a vapor dryer chamber and at least one heater disposed within the vapor dryer chamber. The heater creates a drying medium vapor by heating a liquid form of drying medium within the vapor dryer chamber. At least one cooling coil is preferably disposed within the vapor dryer chamber to condense the drying medium vapor. A vapor monitor may be disposed within the vapor dryer chamber to measure vapor concentration within the vapor dryer chamber. The vapor monitor is preferably connected to a controller that evaluates vapor concentration measurements from the vapor monitor. More specifically, the vapor monitor may be an isopropyl alcohol vapor concentration monitor.
In another aspect of the present invention, the drying medium vapor forms a vapor cloud having a desired steady state blanket level within the vapor dryer chamber. The vapor monitor is preferably positioned to measure the drying medium vapor concentration at the desired steady state blanket level.
In another aspect of the present invention, a vapor dryer control system is disclosed for use in semiconductor fabrication. The vapor dryer control system includes a vapor monitor to measure vapor concentration in a vapor dryer chamber and a controller associated with the vapor monitor to evaluate vapor concentration measurements from the vapor monitor. More specifically, the controller may determine a vapor dryer process cycle end point. More specifically, the controller may detect and note a vapor dryer process excursion.
In yet another aspect of the present invention a method for monitoring a vapor drying process includes providing a vapor monitor in a vapor dryer chamber. The vapor monitor then measures vapor concentration at a selected level of the vapor dryer chamber. The vapor concentration measurements are recorded and used to control the vapor drying process. More specifically, measuring vapor concentration may include measuring the vapor concentration of isopropyl alcohol within the vapor dryer chamber.